You can upgrade as a regular version, but you will have to manually tweak some files in /var/www/html/fop2, as the .tar.gz version includes an index.html while Elastix uses a custom index.php that will always take precedence. The elastix version has the index.html file renamed as fop2.html, so after upgrading from tarball, you will have to rename index.html to fop2.html.